Functional Characterization of Adenosine Receptors and Coupling to ATP-Sensitive K+ Channels in Guinea Pig Urinary Bladder Smooth Muscle

• Published in: The Journal of pharmacology and experimental therapeutics Vol. 300; no. 3; pp. 910 - 917
• Main Authors: Gopalakrishnan, Sujatha M, Buckner, Steven A, Milicic, Ivan, Groebe, Duncan R, Whiteaker, Kristi L, Burns, David J, Warrior, Usha, Gopalakrishnan, Murali
• Format: Journal Article
• Language: English
• Published: United States American Society for Pharmacology and Experimental Therapeutics 01.03.2002
• Subjects: Adenosine - pharmacology; Adenosine Deaminase - pharmacology; Adenylyl Cyclases - metabolism; Animals; ATP-Binding Cassette Transporters; Glyburide - pharmacology; Guinea Pigs; In Vitro Techniques; KATP Channels; Male; Membrane Potentials - drug effects; Membrane Potentials - physiology; Muscle Relaxation - drug effects; Muscle Relaxation - physiology; Muscle, Smooth - drug effects; Muscle, Smooth - metabolism; Potassium Channels - drug effects; Potassium Channels - metabolism; Potassium Channels, Inwardly Rectifying; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Receptor, Adenosine A2A; Receptors, Purinergic P1 - drug effects; Receptors, Purinergic P1 - metabolism; Urinary Bladder - drug effects; Urinary Bladder - metabolism; Vasodilator Agents - pharmacology
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1124/jpet.300.3.910

Although multiple adenosine receptors have been identified, the subtype and underlying mechanisms involved in the relaxation response to adenosine in the urinary bladder remain unclear. The present study investigates changes in the membrane potential, as assessed by fluorescence-based techniques, of bladder smooth muscle cells by adenosine receptor agonists acting via ATP-sensitive potassium (K ATP ) channels. Membrane hyperpolarization evoked by adenosine and various adenosine receptor subtype-selective agonists was attenuated or reversed by the K ATP channel blocker glyburide. Comparison of adenosine receptor agonist potencies eliciting membrane potential effects showed a rank order of potency 5′- N -ethyl-carboxamido adenosine (NECA; −log EC 50 = 7.97) ∼ 2- p -(2-carboxethyl)phenethyl-amino-5′- N -ethylcarboxamidoadenosine hydrochloride (CGS-21680; 7.65) > 2-chloro adenosine (5.90) ∼ 2-chloro- N 6 -cyclopentyladenosine (CCPA; 5.51) ∼ N 6 -cyclopentyladenosine ∼ N 6 -( R )-phenylisopropyladenosine > 2-chloro- N 6 -(3-iodobenzyl)-adenosine-5′- N -methyl-carboxamide (2Cl-IBMECA; 4.78). Membrane potential responses were mimicked by forskolin, a known activator of adenylate cyclase, and papaverine, a phosphodiesterase inhibitor. The A 2A -selective antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3- a ][1,3,5]triazin-5-yl-amino] ethyl)phenol (ZM-241385), and the adenylate cyclase inhibitor N -( cis- 2-phenyl-cyclopentyl) azacyclotridecan-2-imine-hydrochloride (MDL-12330A) inhibited the observed change in membrane potential evoked by adenosine and adenosine-receptor agonists. The rank order potency for relaxation of K + -stimulated guinea pig bladder strips, NECA (−log EC 50 = 6.41) ∼ CGS-21680 (6.38) > 2-chloro adenosine (5.90) ≫ CCPA ∼ 2Cl-IBMECA (>4.0) was comparable to that obtained from membrane potential measurements. Collectively, these studies demonstrate that adenosine-evoked membrane hyperpolarization and relaxation of bladder smooth muscle is mediated by A 2A receptor-mediated activation of K ATP channels via adenylate cyclase and elevation of cAMP.